The present invention relates to an improved shielding arrangement for a cathodic arc vapor deposition system.
Vapor deposition as a means for applying a coating to a substrate is a known art that includes processes such as chemical vapor deposition, physical vapor deposition, and cathodic arc vapor deposition. Chemical vapor deposition involves introducing reactive gaseous elements into a deposition chamber containing one or more substrates to be coated. Physical vapor deposition involves providing a source material and a substrate to be coated in an evacuated deposition chamber. The source material is converted into vapor by an energy input, such as heating by resistive, inductive, or electron beam means.
Cathodic arc vapor deposition involves a source material and a substrate to be coated placed in an evacuated deposition chamber. The chamber contains only a relatively small amount of gas. The negative lead of a direct current power supply is attached to the source material (hereinafter referred to as the xe2x80x9ccathodexe2x80x9d) and the positive lead is attached to an anodic member. In many cases, the positive lead is attached to the deposition chamber, thereby making the chamber the anode. An arc initiating trigger, at or near the same potential as the anode, contacts the cathode and subsequently moves away from the cathode. When the trigger is still in close proximity to the cathode, the difference in potential between the trigger and the cathode causes an arc of electricity to extend therebetween. As the trigger moves further away, the arc jumps between the cathode and the anodic chamber. The exact point, or points, where an arc touches the surface of the cathode is referred to as a cathode spot. Absent a steering mechanism, a cathode spot will move randomly about the surface of the cathode.
The energy deposited by the arc at a cathode spot is intense; on the order of 105 to 107 amperes per square centimeter with a duration of a few to several microseconds. The intensity of the energy raises the local temperature of the cathode spot to approximately equal that of the boiling point of the cathode material (at the evacuated chamber pressure). As a result, cathode material at the cathode spot vaporizes into a plasma containing atoms, molecules, ions, electrons, and particles. Positively charged ions liberated from the cathode are attracted toward any object within the deposition chamber having a negative electric potential relative to the positively charged ion. Some deposition processes maintain the substrate to be coated at the same electric potential as the anode. Other processes use a biasing source to lower the potential of the substrate and thereby make the substrate relatively more attractive to the positively charged ions. In either case, the substrate becomes coated with the vaporized material liberated from the cathode. The rate of deposition, the coating density, and the coating thickness can be adjusted to satisfy the needs of the application.
Currently, in production, the arc which is created has a tendency to drift towards the electrical supply and short out the system once vapor deposition takes place. The way this happens is during the coating process, the vapor builds up on various details and creates a path for the arc to follow. Thus, there is needed a way to eliminate or remove the path.
Accordingly, it is an object of the present invention to provide an improved shielding arrangement for a cathodic arc deposition apparatus.
It is a yet another object of the present invention to provide a shielding arrangement as above which sustains the electrical arc on the cathode for a longer period of time.
The foregoing objects are attained by the shielding arrangement of the present invention.
In accordance with the present invention, a shielding arrangement for use with a cathodic arc deposition apparatus including a contactor formed from an electrically conductive material, which contactor has an axially extending shaft, broadly comprises a cup formed from an electrically conductive material surrounding a portion of the contactor and shield means for preventing material from being deposited on the cup. The shield means, in a first aspect, comprises a removable ring shield attached to the cup. The shield means, in a second aspect, also comprises a shield formed from an electrically non-conductive material surrounding the cup and a portion of the contactor shaft.
Other details of the cathodic arc disposable sting shielding of the present invention, as well as other objects and advantages attendant thereto, are set forth in the following detailed description and the accompanying drawings wherein like reference numerals depict like elements.